As disclosed in U.S. Pat. No. 5,362,634, fermentation product A83543 is a family of related compounds produced by Saccharopolyspora spinosa. The family of natural spinosyn compounds that have previously been isolated are described in U.S. Pat. No. 6,274,350 B1 and WO 01/19840, along with their activities in a variety of insect control assays. A number of semi-synthetic spinosyn analogues are also described in U.S. Pat. No. 6,001,981, in which the chemically accessible areas of the spinosyn molecule were successfully substituted in a variety of ways.
The known members of this family have been referred to as factors or components, and each has been given an identifying letter designation. These compounds are hereinafter referred to as spinosyn A, B, etc. The spinosyn compounds are useful for the control of arachnids, nematodes and insects, in particular Lepidoptera and Diptera species, and they are quite environmentally friendly and have an appealing toxicological profile. The commercial product Spinosad is a mixture of spinosyns A and D (Pesticide Manual, 11th ed., p. 1272). Tables 1 and 2 identify the structures of some known spinosyn compounds:
TABLE 1 FactorR1R2R3R4R5R6R7spinosyn AHCH3C2H5CH3CH3CH3 spinosyn BHCH3C2H5CH3CH3CH3 spinosyn CHCH3C2H5CH3CH3CH3 spinoxyn DCH3CH3(a)C2H5CH3CH3CH3spinosyn EHCH3(a)CH3CH3CH3CH3spinosyn FHH(a)C2H5CH3CH3CH3spinosyn A 17-HCH3HC2H5CH3CH3CH3Psaspinosyn D 17-CH3CH3HC2H5CH3CH3CH3Psaspinosyn E 17-HCH3HCH3CH3CH3CH3Psaspinosyn F 17-HHHC2H5CH3CH3CH3Psa
TABLE 2 FactorR1R2R3R4R5spinoxyn A 9- PsaHCH3C2H5H spinosyn D 9-CH3CH3(a)C2H5HPsaspinosyn AHCH3HC2H5Haglyconespinosyn DCH3CH3HC2H5Haglycone
The naturally produced spinosyn compounds consist of a 5,6,5-tricylic ring system, fused to a 12-membered macrocyclic lactone, a neutral sugar (rhamnose) and an amino sugar (forosamine) (see Kirst et al. (1991). If the amino sugar is not present the compounds have been referred to as the pseudoaglycone of A, D, etc., and if the neutral sugar is not present then the compounds have been referred to as the reverse pseudoaglycone of A, D, etc. A more preferred nomenclature is to refer to the pseudoaglycones as spinosyn A 17-Psa, spinosyn D 17-Psa, etc., and to the reverse pseudoaglycones as spinosyn A 9-Psa, spinosyn D 9-Psa, etc.
The naturally produced spinosyn compounds may be produced via fermentation from cultures NRRL 18395, 18537, 18538, 18539, 18719, 18720, 18743 and 18823. These cultures have been deposited and made part of the stock culture collection of the Midwest Area Northern Regional Research Center, Agricultural Research Service, United States Department of Agriculture, 1815 North University Street, Peoria, Ill. 61604.
U.S. Pat. No. 5,362,634 and corresponding European Patent Application No. 375316 A1 disclose spinosyns A, B, C, D, E, F, G, H, and J. These compounds are disclosed as being produced by culturing a strain of the novel microorganism Saccharopolyspora spinosa selected from NRRL 18395, NRL 18537, NRRL 18538, and NRRL 18539.
WO 93/09126 disclosed spinosyns L, M, N, Q, R, S, and T. Also disclosed therein are two spinosyn J producing strains: NRRL 18719 and NRRL 18720, and a strain that produces spinosyns Q, R, S, and T: NRRL 18823.
WO 94/20518 and U.S. Pat. No. 5,670,486 disclose spinosyns K, O, P, U, V, W, and Y, and derivatives thereof. Also disclosed is spinosyn K-producing strain NRRL 18743.
WO 01/19840 discloses spinosyn analogs produced by culturing Saccharopolyspora species LW107129 (NRRL 30141).
WO 99/46387 and U.S. Pat. No. 6,143,526 disclose the spinosyn biosynthetic genes from Saccharopolyspora spinosa. 
The nature of the genes involved in spinosyn biosynthesis, together with previous studies of precursor incorporation (Broughton et al., 1991), indicate that spinosyns are produced by the stepwise condensation of 2-carbon and 3-carbon carboxylic acids to generate a polyketide that is cyclized and bridged. The tetracyclic, aglycone product of these reactions is converted to the pseudoaglycone by addition of a rhamnosyl residue, and synthesis is completed by the addition of the di-N-methylated sugar, forosamine. In some aspects, this process is similar to the biosynthetic pathway by which other macrolides (such as the antibiotic erythromycin, the antihelmintic avermectin, and the immunosuppressant rapamycin) are produced. In particular, the polyketide nucleus is assembled by a very large, multifunctional protein that is a Type I polyketide synthase (spn PKS). This polypeptide complex comprises a loading module and ten extension modules, each module being responsible for both the addition of a specific acyl-CoA precursor to the growing polyketide chain, and for the degree of reduction of the β-keto carbonyl group. Each module performs several biochemical reactions which are carried out by specific domains of the polypeptide. All the extension modules contain an acyl transferase (AT) domain that donates the acyl group from a precursor to an acyl carrier protein (ACP) domain, and a β-ketosynthase (KS) domain that adds the pre-existing polyketide chain to the new acyl-ACP by decarboxylative condensation. Additional domains are present in some extension modules: β-ketoreductase (KR) domains reduce β-keto groups to hydroxyls, dehydratase (DH) domains remove hydroxyls to leave double bonds, and the enoyl reductase (ER) domain reduces a double bond to leave a saturated carbon. The loading module of the spn PKS is different from the extension modules in that it contains a variant KS domain (KSq), as well as AT and ACP domains. The KSq domain, which is also found in some other Type I PKS loading modules (but not all), is believed to provide the requisite starter unit by decarboxylation of an ACP-bound acyl chain (Bisang et al., 1999). The terminal extension module contains a thioesterase/cyclase (TE) domain that liberates the polyketide chain from the PKS.
The spinosyn PKS DNA region consists of 5 ORFs with in-frame stop codons at the end of some ACP domains, similar to the PKS ORFs in the other macrolide-producing bacteria. The five spinosyn PKS genes are arranged head-to-tail, without any intervening non-PKS functions such as the insertion element found between the erythromycin PKS genes AI and AII (Donadio et al., 1993). They are designated spnA, spnB, spnC, spnD, and spnE. The nucleotide sequence for each of the five spinosyn PKS genes, and the corresponding polypeptides, are identified in U.S. Pat. No. 6,143,526 and in Waldron et al., 2001. Also identified in these sources are the predicted translation products of the PKS genes, and the boundaries of the domains and modules.
After it is synthesized, the spinosyn polyketide precursor condenses to form a macrocyclic lactone, referred to hereinafter as the polyketide nucleus. Production of insecticidally-active spinosyns requires additional processing of the polyketide nucleus. First, carbon-carbon bridges must be formed between C3 and C14, C4 and C12, and C7 and C11, to generate the aglycone intermediate. Possible mechanisms for these unusual reactions have been suggested (Waldron et al., 2001), but the structural features of the polyketide substrate that are required for them to occur are not known. Second, a tri-O-methyl rhamnose must be incorporated at C9 to generate the pseudoaglycone. It is not known if the rhamnose is normally methylated before or after its addition to the aglycone, but S. spinosa is capable of adding the methyl groups after the rhamnose moiety has been conjugated to the aglycone (Broughton et al., 1991). The methylations must occur in a particular sequence (2′ then 3′ then 4′) or not all of them will take place, indicating that the methyltransferases have very specific substrate requirements. The third processing step, addition of forosamine at C17, is needed to produce the most active spinosyns. The enzymes involved in this step also have stringent substrate requirements: the forosaminyl transferase will not use the aglycone as a substrate, and the N-methyltransferase will not act on the forosamine after it has been attached to the pseudoaglycone. This substrate-specificity of later biosynthetic enzymes may be a barrier to producing novel, biologically-active spinosyns from precursors with different chemical structures.
In certain cases polyketide synthase (PKS) genes have previously been manipulated with the objective of providing novel polyketides. In-frame deletion of the DNA encoding part of the KR domain in module 5 of the erythromycin-producing (ery) PKS has been shown to lead to the formation of erythromycin analogues, namely 5,6-dideoxy-3alpha-mycarosyl-5-oxoerythronolide B and 5,6-dideoxy-5-oxoerythronolide B (Donadio et al., 1991). Likewise, alteration of active site residues in the ER domain of module 4 of the ery PKS, by genetic engineering of the corresponding PKS-encoding DNA and its introduction into Saccharopolyspora erythraea, led to the production of 6,7-anhydroerythromycin C (Donadio et al., 1993). WO 93/13663 describes additional types of genetic manipulation of the ery PKS genes that are capable of producing altered polyketides.
WO 98/01546 discloses replacement of the loading module of the ery PKS with the loading module from the avermectin (dye) PKS, to produce a hybrid Type I PKS gene that incorporates different starter units to make novel erythromycin analogues.
However, it has also been found that not all manipulations of PKS genes produce the targeted new analogues. When Donadio et al. (1993) inactivated an ER domain of the ery PKS, the resulting anhydro-derivative could not be completely processed because it was no longer a substrate for the mycarose-O-methyltransferase. Changing the polyketide starter unit prevented complete elongation and elaboration of a rifamycin analogue in Amycolatopsis mediterranei (Hunziker et al., 1998). Given the extensive substrate-specific processing that is required to generate insecticidally-active spinosyns, it is not obvious that genetic modifications which change the structure of a spinosyn polyketide will permit synthesis of a fully-processed molecule with useful biological activity. However, if such analogues could be made, and they had a different spectrum of insecticidal activity, they would be highly desirable because known spinosyns do not control all pests.